Australian cities need to prepare for more frequent, intense and longer-lasting heatwaves, experts say, which could lead to restrictions on black roads and roofs that contribute to dangerous heat traps.

Heatwaves already kill more Australians than bushfires and cyclones and meteorologists say a looming El Nino weather system could push up summer temperatures later this year.

Scientists are investigating ways to lower the temperatures of Australian cities, including using light-coloured bitumen, planting more trees and floating the idea of banning black roofs.

"Australians regularly overestimate their ability to withstand extreme heat," Professor Liz Hanna, an environmental health expert from the Australian National University, told Lateline.

"We think we know how to handle it because we live in a hot country but we're now dealing with unprecedented extremes.

"We have to take heat as a health issue far more seriously."

Extreme heat 'could kill hundreds in a few days'

By 2050, an extreme heat event in Melbourne could kill more than 1,000 people in a few days unless there is better preparation, according to a Federal Government report looking at extreme heat events.

"We drive around and shake our heads in dismay at the silliness of this, the cost of retrofitting these houses and the poor, miserable people in the future who will have high electricity bills because they'll be forced to cool their houses artificially," she said.

The worst-affected cities include Perth, Adelaide, Melbourne and Sydney's western suburbs which endure drier and more intense heat extremes.

Professor Tapper and other researchers have determined the maximum temperature threshold beyond which death rates spike. It is different in each city because people acclimatise to local conditions.

Overnight minimum temperatures also have a significant impact on death rates.

City

Maximum temperature threshold for excess mortality (degrees Celsius)

Canberra

33

Hobart

35

Brisbane

36

Darwin

37

Sydney

38

Melbourne

39

Adelaide

42

Perth

44

(Source: National Climate Change Adaptation Research Facility)

The Melbourne City Council and other academic researchers assessed the 2009 heatwaves - that included three days over 43C – and found there were 374 deaths during the period.

There were also more than 1,000 other emergency callouts, blackouts, mass public transport strandings and bushfires costing hundreds of millions of dollars.

Heatwaves are also linked to more episodes of mental illness, foodborne disease and violence.

"We had a reminder of that just last summer when we had a whole week over 40 degrees and again public transport tracks buckled, we had people stuck in lifts all over the city and outdoor sites shut down," he said.

"You get the feeling that we're only one step away from real trouble in a heatwave."

Trees can cool cities

However, almost all of these impacts, including deaths, are preventable with deliberate planning to cool cities.

The right kind of design could enable cities to offset up to four degrees Celsius - which is one of the upper projections for global warming.